1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method.
2. Description of the Related Art
A process of manufacturing a micropatterned semiconductor device such as an LSI or VLSI adopts a reduction projection exposure apparatus which reduces the pattern of an reticle and projects and transfers it onto a substrate coated with a photosensitive agent. Along with an improvement in packaging density of semiconductor devices, further micropatterning is becoming necessary. The exposure apparatus has coped with the micropatterning along with the development of the resist process.
To improve the resolving power of the exposure apparatus, there are a method of shortening the exposure wavelength and a method of increasing the numerical aperture (NA) of a projection optical system.
To practice the method of shortening the exposure wavelength, various light sources are under development. That is, the exposure wavelength is shifting from the 365-nm i-line to a ArF excimer laser oscillation wavelength of about 193 nm. An exposure apparatus using the Extreme Ultra Violet beam (EUV beam) with a smaller wavelength of 10-15 nm than ultraviolet wavelength are also under development.
To practice the method of increasing the numerical aperture (NA) of a projection optical system, a projection exposure technique using an immersion method is receiving a great deal of attention. The immersion method is used to perform projection exposure while the space between the final surface of a projection optical system and the surface of a substrate (e.g., a wafer) is filled with a liquid instead of a gas, unlike a conventional method. The immersion method has an advantage of improving the resolving power as compared with the conventional method even when a light source used has the same wavelength as that in the conventional method.
Assume that a liquid supplied to the space between a projection optical system and a wafer is pure water (refractive index: 1.33), and the maximum incident angle of a light beam applied on the wafer in the immersion method is equal to that in the conventional method. In this case, as the NA of the projection optical system in the immersion method is 1.33 times that in the conventional method, the resolving power in the immersion method improves to 1.33 times that in the conventional method.
In this manner, the immersion method can obtain a resolving power corresponding to NA≧1, which is impossible in the conventional method. To achieve the immersion method, various exposure apparatuses are proposed.
Japanese Patent Laid-Open No. 2005-19864 proposes an exposure apparatus which comprises a liquid supply nozzle arranged around a projection optical system in a first direction when seen from it, and a flat plate (top plate) arranged on a substrate stage to be nearly flush with the surface of a substrate to hold an immersion region. This exposure apparatus supplies a liquid onto the substrate surface via the liquid supply nozzle when the substrate stage moves the substrate in a second direction opposite to the first direction. The liquid is continuously supplied onto the substrate surface via the liquid supply nozzle so that a liquid film extends continuously as the substrate moves. This makes it possible to surely fill the space between the substrate surface and the final surface of the projection optical system with the liquid.
Japanese Patent Laid-Open No. 2005-116570 proposes an exposure apparatus which comprises a light-receiving unit for receiving light which has passed though a projection optical system via a slit plate arranged on the image plane of the projection optical system, and a temperature sensor for detecting the temperature information of a liquid which fills the space between the projection optical system and the slit plate. This exposure apparatus irradiates and exposes a substrate arranged on the image plane side of the projection optical system, with exposure light via the projection optical system and liquid. Using the detection result obtained by the light-receiving unit and the measurement result obtained by the temperature sensor, this apparatus calculates performance information including the imaging performance. This allows accurate exposure processing by satisfactorily performing exposure state optimization processing on the basis of the light-receiving result obtained by the light-receiving unit.
Japanese Patent Laid-Open No. 2005-191557 proposes an exposure apparatus which comprises a substrate table for holding a substrate and a plate member which is exchangeably arranged on the substrate table and has a liquid-repellent flat surface. This makes it possible to prevent the liquid from remaining on the substrate table.
Japanese Patent Laid-Opens No. 2005-19864 disclose a rectangular measurement member. The rectangular measurement member rotates relative to a top plate when being assembled on a substrate stage. Then, the width of the gap between the opening side surface of the top plate and the outer surface of the measurement member readily changes depending on the gap position. Assume here that a liquid supplied to the space between a projection optical system and a wafer nonuniformly enters the gap. In this case, the temperature drop of the liquid due to its vaporization heat varies, so the thermal deformation amount of the measurement member also varies. This may result in a decrease in the accuracy of measurement using a reference mark.
When a drainage unit for draining the liquid which has entered the gap between the opening side surface of the top plate and the outer surface of the measurement member is formed in the measurement member, the easiness of mounting of the drainage unit may be limited.
Japanese Patent Laid-Open No. 2005-19864, No. 2005-116570, and No. 2005-191557 does not disclose a concrete structure to prevent a liquid which has entered the gap between the opening side surface of the top plate and the outer surface of the measurement member from reaching the substrate stage.